EP1573664B1 - Device for determining the energy level of an energy store of a mobile data carrier - Google Patents

Abstract

The battery charge level detection device uses an evaluation circuit (8) connected to the battery (7), containing an auxiliary capacitor (13) and a measuring circuit (15,16,21) for measuring the charge time of the auxiliary capacitor, its output fed to an evaluation logic (18) providing the battery charge. The voltage provided by the battery is fed to a voltage stabilization stage for supplying the data carrier, the measuring circuit coupled to the battery via a current reflector (11,12) with 2 parallel paths, one containing the auxiliary capacitor, the measuring circuit and the evaluation logic, the other containing an ohmic resistor (14).

Description

Device for determining the determination of the energy state of an energy storage of a mobile data carrier

The invention relates to a device for determining the energy state of an energy storage of a mobile data carrier. Such a device can be used, for example, in connection with contactless identification systems.

Contactless identification systems work on the basis of non-contact transmission technologies. These can be based on an electromagnetic transmission or a transmission by means of light, infrared or ultrasonic signals. Systems of this type are used for example for the identification of persons or moving goods such as means of transport. The necessary data is to be transmitted from a transceiver via a non-contact data link, for example via an air interface to a disk and back. In this case, the non-contact identification technology also allows detection of data during a passing movement of the data carrier on the transceiver, without the data carrier has to be inserted into a read / write device or pulled through this. Data carriers of this kind are used, for example, as tickets with an electronically rechargeable credit, the respective amount being debited automatically when using the means of transport.

From DE 691 23 887 T2 an IC card is known, which can detect a voltage drop of the built-in battery. The IC card has, inter alia, a data transmission / reception device, a data processing device, a charging device, a comparison device and a time measuring device.

From DE 100 54 970 A1 a method for controlling the charging and discharging phases of a backup capacitor is known. In a circuit arrangement, a constant current source is formed by a current mirror circuit and compared via a comparator, the voltage on the backup capacitor with a bandgap reference.

In order that the data carriers can be used indefinitely, they do not require the integration of chemical energy stores, such as batteries. The necessary electrical energy of the disk is therefore externally, d. H. taken from an originating from the transceiver energy source, such as an electric or magnetic field, contactless. For communication of the transceiver with such data carriers, therefore, suitable transmission and coding methods are necessary. On the one hand, only certain frequency bands are usually released for the transmission of data, for example the ISM frequency bands (Industrial, Scientific & Medical) for industrial, scientific and medical applications. Possible national radio regulations can specify, among other things, the modulation bandwidths to be maintained and the field strengths. On the other hand, the transmission and coding methods must also ensure an energetic supply of the electronics on the data carrier.

Such methods are described in the ISO / IEC 15693 Part 2 "Air Interface and Initialization" standard. Methods of this type allow a continuous power supply of the disk electronics, which comes from the energy of the applied carrier frequency of the transceiver. The carrier frequency is switched off for the modulation of the data to be transmitted only for a maximum time interval. Within this time interval a previously charged by the electric or magnetic field energy storage must be able to make the power supply of the disk electronics. As a temporary energy storage on the disk is generally a capacitor is used. The data is coded by switching off the carrier at fixed positions within a cyclic time grid. The standard also sets the field strength limits for the modulation-induced sidebands at a given carrier frequency, taking into account the above-mentioned maximum time interval. For the amount of sideband modulation on the one hand, the time ratio of switched on to off carrier frequency prevail. In addition, consecutive changes from on to off carrier frequency continue to contribute to a significant increase in sideband modulation. The need to comply with the sideband limits specified in the standard results in a maximum possible data rate.

However, data transmission in non-contact transmission techniques may be undesirably affected by insufficient coupling. Such an insufficient coupling can be present, for example, when a mobile data carrier moves very quickly through a field, or even at the field boundaries, where the energy transfer is low.

This can lead to disadvantages, for example, if a write operation to a read / write memory of a mobile data carrier was started in the presence of sufficient coupling between the mobile data carrier and the stationary read / write device, but due to a relative movement of the mobile data carrier to the stationary one Read / write device sufficient recharge the energy storage of the mobile data carrier can not be made. This can result in the energy required for the writing process not being available in the mobile data carrier, so that the writing process can not be ended correctly.

The object of the invention is to show a way how the disadvantages described above can be avoided.

This object is achieved by a device having the features specified in claim 1. Advantageous embodiments and developments of the invention will become apparent from the dependent claims 2-7. The claim 8 relates to the use of the device according to the invention in a mobile data carrier. Claim 9 relates to the use of the device according to the invention in an identification system.

The advantages of the invention are, in particular, that information about the energy state of the mobile data carrier can be made available to the user at any desired time. Thus, it is possible to detect an insufficient energy state of the energy storage device of the mobile data carrier and to correctly and completely perform a data exchange that is incomplete or faulty due to the insufficient energy state. This option can be implemented on the mobile data carrier with only a small additional effort. A device according to the invention provides fast and good information about the energy state of the energy storage of the mobile data carrier. Another advantage of the invention is an almost complete independence of the obtained statements of tolerances involved circuit elements.

Further advantageous features of the invention will become apparent from the exemplary explanation with reference to FIGS.

Figur 1

ein Blockschaltbild, in welchem die zum Verständnis der Erfindung wesentlichen Bestandteile eines Identifikationssystems dargestellt sind,

Figur 2

ein Schaltbild, in welchem eine Vorrichtung zur Ermittlung des Energiezustandes eines Energiespeichers eines mobilen Datenträgers dargestellt ist,

Figur 3

ein Diagramm zur Veranschaulichung verschiedener Spannungen,

Figur 4

ein Diagramm zur Veranschaulichung des Spannungsverlaufs der am Kondensator 7 von Figur 2 anliegenden Spannung U1 in Abhängigkeit vom Abstand zwischen dem Schreib-/Lesegerät und dem mobilen Datenträger,

Figur 5

ein Diagramm zur Veranschaulichung der Lage zweier Messzeitpunkte,

Figur 6

ein Diagramm zur Veranschaulichung der gemessenen Ladezeiten bei einer Messung zum ersten Messzeitpunkt, zu welchem eine vergleichsweise kleine Spannung am Kondensator 7 anliegt, und

Figur 7

ein Diagramm zur Veranschaulichung der gemessenen Ladezeiten bei einer Messung zum zweiten Messzeitpunkt, zu welchem eine vergleichsweise hohe Spannung am Kondensator 7 anliegt.

It shows

FIG. 1

1 is a block diagram in which the components of an identification system essential for understanding the invention are shown,

FIG. 2

a circuit diagram in which a device for determining the energy state of an energy storage of a mobile data carrier is shown,

FIG. 3

a diagram illustrating different voltages,

FIG. 4

a diagram illustrating the voltage curve of the voltage applied to the capacitor 7 of Figure 2 U1 as a function of the distance between the read / write device and the mobile data carrier,

FIG. 5

a diagram for illustrating the position of two measurement times,

FIG. 6

a diagram illustrating the measured charging times in a measurement at the first measurement time, to which a comparatively small voltage applied to the capacitor 7, and

FIG. 7

a diagram illustrating the measured charging times in a measurement at the second measuring time, to which a comparatively high voltage applied to the capacitor 7.

FIG. 1 shows a block diagram in which the components of an identification system essential for understanding the invention are shown.

The system shown has a read / write device 1 and a mobile data carrier 4. Furthermore, a bidirectional exchange of data D takes place via an air transmission path 3 between the read / write device 1 and the mobile data carrier 4. Furthermore, the read / write device also transmits energy E to the mobile data carrier 4 via the air transmission path 3, this transmission of energy into Time intervals are made in which no exchange of data takes place. The transmission of data and energy is based on the principle of inductive coupling. For this purpose, the read / write device 1 is provided with a coil 2 and the mobile data carrier 4 with a coil 5.

In the mobile data carrier 4, the transmitted energy via a rectifier 6 is fed to a realized as a capacitor energy storage. The voltage applied to the capacitor 7 unstabilized DC voltage is fed to a voltage stabilizer 9, at the output of which the supply of the mobile data carrier 4 required stabilized DC voltage is provided.

Furthermore, the capacitor 7 is connected to a device 8, which is provided for determining the energy state of the capacitor 7.

2 shows a circuit diagram in which the device 8 for determining the energy state of the capacitor 7 of the mobile data carrier 4 is shown in more detail. The device 8 has a current mirror 11 comprising transistors 11 and 12. This has two parallel paths. In the first path, in which the transistor 12 is located, a current I _{0 flows} . In the second path, in which the transistor 11 is arranged, a current I _{R flows} . In the second path there is further provided an ohmic resistor 14 connected to the transistor 11, the other terminal of which is connected to a HIGH / LOW level signal input 20 of the device 8. About this input 20 of the device 8 is supplied by a logic, not shown, either a high-level signal or a low-level signal.

In the first path, an auxiliary capacitor 13 is connected to the transistor 12, whose other terminal is grounded. The ground remote terminal of the auxiliary capacitor 13 is connected to an input of an EX-OR gate 16 and to the collector of an NPN transistor 15. The emitter of the transistor 15 is grounded. The base of the transistor 15 is connected via an ohmic resistor 21 to an input 17 of the device 8. The input 17 is a measuring time input, via which the device 8 signals are supplied, which define measuring time intervals. These measurement time signals are generated in the aforementioned logic, not shown, which also provides the signals provided at the HIGH-LOW level signal input 20 available. In this logic is information about the system clock, which are needed to generate the inputs 17 and 20 supplied signals. The measuring input signals applied to the input 17 are supplied to the other input of the EX-OR gate 16 and the ohmic resistor 21 of the base of the npn transistor 15.

The output signals of the EX-OR element 16, which is information about charging times of the auxiliary capacitor 13, are fed to an evaluation logic 18. From the said charging times, this calculates a quantity in the form of a numerical value, which gives information about the energy state of the capacitor 7. In particular, this numerical value contains information about the ratio of the unstabilized supply voltage applied to the capacitor 7 to the stabilized DC voltage required by the mobile data carrier as the supply voltage. The latter is for example 3 V and is the operating voltage of a chip of the mobile data carrier. On the basis of the present at the output of the evaluation logic 18 information can be made in particular a statement about how large the energy reserve of the mobile data carrier at the time of measurement.

The mode of operation of the device shown in FIG. 2 will be explained in more detail below.

In the case of a current mirror, as implemented by transistors 11 and 12 in FIG. 2, the following general relationship applies: $$\frac{{\mathrm{I}}_0}{{\mathrm{I}}_{\mathrm{R}}}=1-\frac{2}{\mathrm{\beta }+2}\approx 1.$$

Furthermore, for the voltage U of a capacitor C, which is charged with a constant current I ₀ , the following relationship applies: $$\mathrm{U}={\mathrm{<figure-callout\; id="0"\; label="I"\; filenames="imgf0001.png"\; state="\{\{state\}\}">I</figure-callout>}}_0·\mathrm{t}/\mathrm{C},$$

From this relationship follows by conversion: $$\mathrm{t}=\mathrm{U}·\mathrm{C}/{\mathrm{I}}_0,$$

These relationships also apply to the charging process of the auxiliary capacitor 13 and are taken into account in the inventive determination of the energy state of the capacitor 7.

If, referring to FIG. 2, the voltage dropping across the capacitor 7 is denoted by U1, the voltage dropping at the transistor 11 to U2, the voltage dropping at the resistor 14 to U3 and the voltages provided by the input 20 to UH or UL, then:
U3 = U1-U2-UL, if UL is present at input 20, and
U3 = U1 - U2 - UH if UH is present at input 20.

If UL = 0, then: $$\mathrm{U}3=\mathrm{U}1-\mathrm{U}\mathrm{Second}$$

For the current I _R , if UH is present at input 20, the following relationship applies: $${\mathrm{I}}_{\mathrm{R}\left(\mathrm{U}\mathrm{H}\right)}=\frac{\mathrm{U}3-\mathrm{<figure-callout\; id="14"\; label="U\; H\; R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">U\; </figure-callout>}\mathrm{H}}{{\mathrm{R}}_{}},$$

If UL is present at input 20, the following applies to the current I _R : $${\mathrm{I}}_{\mathrm{R}\left(\mathrm{U}\mathrm{L}\right)}=\frac{\mathrm{U}3-\mathrm{<figure-callout\; id="14"\; label="U\; L\; R"\; filenames="imgf0001.png"\; state="\{\{state\}\}">U\; </figure-callout>}\mathrm{L}}{{\mathrm{R}}_{}},$$

For UL = 0 follows: $$\frac{{\mathrm{I}}_{\mathrm{R}\left(\mathrm{U}\mathrm{L}\right)}}{{\mathrm{I}}_{\mathrm{R}\left(\mathrm{U}\mathrm{H}\right)}}=\frac{\mathrm{U}3}{\mathrm{U}3-\mathrm{U}\mathrm{H}},$$

Consequently, in a quotient of the currents I _{R (UL)} and I _{R (UH),} the value of the resistor 14 is eliminated.

$${\mathrm{I}}_0\approx {\mathrm{I}}_{\mathrm{R}};$$

$${\mathrm{t}}_{\mathrm{U}\mathrm{H}}=\frac{{\mathrm{C}}_{13}·{\mathrm{U}}_{\mathrm{t}\mathrm{h}}}{{\mathrm{I}}_{\mathrm{R}\left(\mathrm{U}\mathrm{H}\right)}};$$

$${\mathrm{t}}_{\mathrm{U}\mathrm{L}}=\frac{{\mathrm{C}}_{13}·{\mathrm{U}}_{\mathrm{t}\mathrm{h}}}{{\mathrm{I}}_{\mathrm{R}\left(\mathrm{U}\mathrm{L}\right)}}.$$

Considering Equation 1 and Equation 2, the following relationships are obtained for the device shown in FIG. 2: $$\mathrm{t}=\frac{{\mathrm{<figure-callout\; id="13"\; label="C"\; filenames="imgf0001.png"\; state="\{\{state\}\}">C</figure-callout>}}_{13}·\mathrm{U}4}{{\mathrm{I}}_0};$$

$${\mathrm{I}}_0\approx {\mathrm{I}}_{\mathrm{R}};$$

$${\mathrm{t}}_{\mathrm{U}\mathrm{H}}=\frac{{\mathrm{<figure-callout\; id="13"\; label="C"\; filenames="imgf0001.png"\; state="\{\{state\}\}">C</figure-callout>}}_{13}·{\mathrm{U}}_{\mathrm{t}\mathrm{H}}}{{\mathrm{I}}_{\mathrm{R}\left(\mathrm{U}\mathrm{H}\right)}};$$

$${\mathrm{t}}_{\mathrm{U}\mathrm{L}}=\frac{{\mathrm{<figure-callout\; id="13"\; label="C"\; filenames="imgf0001.png"\; state="\{\{state\}\}">C</figure-callout>}}_{13}·{\mathrm{U}}_{\mathrm{t}\mathrm{H}}}{{\mathrm{I}}_{\mathrm{R}\left(\mathrm{U}\mathrm{L}\right)}},$$

It follows: $$\frac{{\mathrm{t}}_{\mathrm{U}\mathrm{H}}}{{\mathrm{t}}_{\mathrm{U}\mathrm{L}}}=\frac{{\mathrm{I}}_{\mathrm{R}\left(\mathrm{U}\mathrm{L}\right)}}{{\mathrm{I}}_{\mathrm{R}\left(\mathrm{U}\mathrm{H}\right)}}=\frac{\mathrm{U}3}{\mathrm{U}3-\mathrm{U}\mathrm{H}}$$

In this case, t _UH and t _UL charging times of the auxiliary capacitor 13 in the case of a charge of this capacitor with the currents I _{R (UH)} and I _{R (UL)} until the voltage _threshold U _th at the input of the EX-OR element is reached. In this case, it was assumed as an input condition that the auxiliary capacitor 13 is in each case completely discharged via the conducting transistor 15 before the start of a measuring operation, as will be explained below in connection with FIGS. 6 and 7.

It can be seen from equation 3 that neither the capacitance value of the auxiliary capacitor 13 nor the voltage value of the threshold voltage U _{th have} any influence on this equation. The charging times t _UH and t _UL are inversely proportional to the charging currents I _{R (UH)} and I _{R (UL)} .

The useful scope of Equation 3 is the range of UH << U3 and U3-UH> 0.

FIG. 3 shows a diagram for illustrating different voltages of FIG. 2. Along the abscissa, the distance S of the read / write device 1 from the mobile data carrier 4 and along the ordinate the inductive coupling or the coupling factor k are plotted. It can be seen that the LOW level signal UL and the HIGH level signal UH are each constant regardless of the distance S and that the voltage U1, which is applied to the capacitor 7, becomes smaller with increasing distance S.

$$\mathrm{U}\mathrm{H}\approx {\mathrm{U}}_{\mathrm{CHIP}},$$

wobei U_CHIP die Versorgungsspannung des mobilen Datenträgers 4 ist.From the voltage applied to the capacitor 7, unstabilized voltage U1, the supply voltage of the mobile data carrier 4 is obtained by a taking place in the circuit block 9 of Figure 1 stabilization. It is assumed that the following relationships apply in the lightly loaded state: $$\mathrm{U}\mathrm{L}\approx 0\mathrm{}\mathrm{V}$$

$$\mathrm{U}\mathrm{H}\approx {\mathrm{U}}_{\mathrm{CHIP}}.$$

where U _{CHIP is} the supply voltage of the mobile data carrier 4.

FIG. 4 shows a diagram for illustrating the voltage profile of the unstabilized voltage U1 applied to the capacitor 7 of FIG. 2 as a function of the distance between the read / write device 1 and the mobile data carrier 4. This bell-shaped voltage characteristic also exists when the mobile data carrier 4 at the same distance parallel to the read / write device 1 is passed.

FIG. 5 shows a diagram for illustrating the position of two measuring times or measuring time intervals. If the mobile data carrier 4 is moved parallel to the read / write device 1 at a constant distance S, then the voltage U1 on the capacitor 7 has the illustrated time profile, which is bell-shaped. According to the invention, two arbitrary measurement times or measurement time intervals are defined, wherein the voltage value at the measurement time t1 is comparatively small and relatively large at the measurement time t2. As is apparent from FIGS. 6 and 7, different charging times result at the measuring times from which conclusions can be drawn about the energy state of the capacitor 7 of the mobile data carrier 4 and thus also can be drawn on the working capacity of the mobile data carrier 4.

FIG. 6 shows a diagram for illustrating the measured charging times during a measurement at the first measuring time t1, at which a comparatively small voltage U1 is applied to the capacitor 7. 6 shows the signal UH or UL present at the input 20, an integration time signal in the track b, the measurement time signal applied to the input 17 in the track c, the threshold voltage U _th in the track d and in the track e is applied to the auxiliary capacitor 13 voltage U4.

The signal UH or UL shown in the track a and the measuring time signal shown in the track c are not shown Logic specified in which information about the system clock is available. The measurement time signal is started when the signal shown in track a transitions from the HIGH to the LOW state. At this time, the integration time interval shown in the lane b also starts. As can be seen from the track e, the charging of the auxiliary capacitor 13 by the charging current I _{0 (UL)} begins at this time. The charging process is continued until the voltage across the auxiliary capacitor 13 reaches the threshold voltage U _th shown in the track d. At this time, as can be seen from the lane b, the integration time is terminated and provided as the charging time t _{UL of} the evaluation logic 18. After this time, the measuring time interval is ended, as can be seen from the track c. Immediately after the end of the measuring time interval, the auxiliary capacitor 13 is discharged by the then conducting transistor 15.

If the HIGH-LOW level signal shown in the track a has the HIGH level and the auxiliary capacitor 13 is discharged, then - as is apparent from the second falling edge of the measuring time signal shown in the track c - a second measuring time interval is started. At this time, a measurement of the integration time begins again, as can be seen from the second rising edge of the integration time signal shown in the track b. Furthermore, charging of the auxiliary capacitor 13 by the charging current I _{0 (UH)} also begins at this time. The charging process is continued until the voltage across the auxiliary capacitor 13 reaches the threshold voltage U _th shown in the track d. At this time, as can be seen from the track b, the integration time is ended and provided as the charging time t _{UH of} the evaluation logic 18. If, after this time, the measuring time signal returns to the HIGH state, this measuring time interval is also ended and the auxiliary capacitor 13 is discharged via the then conducting transistor 15.

FIG. 7 shows a diagram for illustrating the measured charging times during a measurement at the second measuring time t 2, at which a comparatively large voltage U 1 is applied to the capacitor 7. 7 shows the signal UH or UL present at the input 20, an integration time signal in the track b, the measurement time signal applied to the input 17 in the track c, the threshold voltage U _th in the track d and in the track e is applied to the auxiliary capacitor 13 voltage U4.

The signal UH or UL shown in the track a and the measuring time signal shown in the track c are given by the unsigned logic in which information about the system clock are present. The measurement time signal is started when the signal shown in track a transitions from the HIGH to the LOW state. At this time, the integration time interval shown in the lane b also starts. As can be seen from the track e, the charging of the auxiliary capacitor 13 by the charging current I _{0 (UL)} begins at this time. The charging process is continued until the voltage across the auxiliary capacitor 13 reaches the threshold voltage U _th shown in the track d. At this time, as can be seen from the lane b, the integration time is terminated and provided as the charging time t _{UL of} the evaluation logic 18. After this time, the measuring time interval is ended, as can be seen from the track c. Immediately after the end of the measuring time interval, the auxiliary capacitor 13 is discharged by the then conducting transistor 15.

If the HIGH-LOW level signal shown in the track a has the HIGH level and the auxiliary capacitor 13 is discharged, then - as is apparent from the second falling edge of the measuring time signal shown in the track c - a second measuring time interval is started. At this time, a measurement of the integration time begins again, as can be seen from the second rising edge of the integration time signal shown in the track b. It also starts to this Time also a charging of the auxiliary capacitor 13 by the charging current I _{0 (UH)} . The charging process is continued until the voltage across the auxiliary capacitor 13 reaches the threshold voltage U _th shown in the track d. At this time, as can be seen from the track b, the integration time is ended and provided as the charging time t _{UH of} the evaluation logic 18. If, after this time, the measuring time signal returns to the HIGH state, this measuring time interval is also ended and the auxiliary capacitor 13 is discharged via the then conducting transistor 15.

The evaluation logic 18 in each case forms the quotient of the charging times t _UL and t _UH and makes these quotients available as the quantity describing the energy state of the capacitor 7 at the output 19 of the device 8. From there it is fed to a transmitting unit of the mobile data carrier 4 and transmitted via the air transmission path 3 to the read / write device 1. There it is available for a display, by means of which a user can assess the energy state of the capacitor 7 of the mobile data carrier 4 and if necessary initiate appropriate measures. Alternatively, the transmitted to the read / write device 1, the energy state of the capacitor 7 descriptive size can also be evaluated by an automatic unit in the read / write device 1, which automatically directs appropriate measures if necessary.

Claims (9)

1. Device for determining the energy state of an energy storing device of a data carrier, in which a stabilised DC voltage for the supply of the data carrier is derived from an unstabilised DC voltage available at the energy storing device, with the device comprising an evaluation circuit connected to the energy storing device, said evaluation circuit containing an auxiliary capacitor and a measurement circuit for measuring the charging times of the auxiliary capacitor, and having an evaluation logic connected to the output of the measurement circuit, said evaluation logic determining a quantity describing the energy state of the energy storing device from the measured charging times of the auxiliary capacitor
   characterised by
   a voltage stabiliser for stabilising the unstabilised DC voltage available at the energy storing device (7), and by the evaluation circuit (8) with a current mirror (11, 12) arranged between the energy storage device (7) and the measurement circuit (15, 16, 21), said current mirror comprising mutually parallel paths, with the measurement circuit (15,16,21) connected to the auxiliary capacitor, and the evaluation logic (18) connected to the output of the measurement circuit (15,16,21) being arranged in the first of these paths of the auxiliary capacitor (13) and with ohmic resistor (14) being arranged in a second path.
2. Device as claimed in claim 1, characterised in that the measurement circuit (15,16,21) has a measurement time signal input (17), via which a measurement time signal is supplied to
   said measurement circuit (15, 16, 21).
3. A device as claimed in claim 2, characterised in that the measurement time signal input (17) is connected to the control input of a transistor (15) of the measurement circuit (15, 16, 21) and with an input of an XOR gate (16) of the measurement circuit (15,16,21), with the transistor (15) in its conducting state grounding the terminal of the auxiliary capacitor (13) remote from the ground.
4. A device as claimed in claim 3, characterised in that the terminal of the auxiliary capacitor (13) remote from the ground is connected to a second input of the XOR gate (16).
5. A device as claimed in one of the preceding claims, characterised in that the measurement circuit (15, 16, 21) has a digital signal input (20) via which a HIGH level signal and a LOW level signal can be supplied to said measurement circuit.
6. A device as claimed in claim 5, characterised in that the ohmic resistor (14) arranged in the second path is disposed between the digital signal input (20) and the current mirror (11, 12).
7. A device as claimed in claim 5 or 6, characterised in that the measurement circuit (15, 16, 21) is provided to measure a first and a second charging time of the auxiliary capacitor (13),
   with the first charging time being determined when a LOW level signal is present at the digital signal input (20) and the second charging time is determined when a HIGH level signal is present at the digital signal input (20).
8. Use of a device as claimed in one of the preceding claims, in a mobile data carrier (4) for the contactless exchange of data with a transceiver (1) comprising transmitting means for sending the quantity describing the energy state of the energy storing device (7) to the transceiver (1).
9. Use of a device as claimed in one of the preceding claims 1 to 7 in an identification system, comprising a transceiver (1) and a mobile data carrier(4) connected to the transceiver via a contactless transmission link (3), with the mobile data carrier (4) comprising the device and the transmitting means for sending the quantity describing the energy state of the energy storing device (7) to the transceiver (1).

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